The present invention relates to the attachment of discs or wheels to shafts, and more particularly, to the attachment of a disc to a shaft in a pulp refiner or similar apparatus.
In attaching wheels to discs or shafts, it is common practice to use keys in keyways and/or thermally-induced interference fit to hold the disc in place and to transmit torque. Examples of such connections appear in FIG. 3 of U.S. Pat. No. 3,260,469, and FIG. 2 of U.S. Pat. No. 4,586,662. In high speed operation, it may be necessary to use a considerable amount of interference fit to compensate for thermal growth and the stretching of the bore opening resulting from centrifugal force. The combination of high thermally-induced interference and a keyway produces high localized stresses in the corners of the keyway, due to the abrupt change in cross-section.
The radius in the corner of the keyway is known to have a considerable influence on the peak stress. In rectangular keyways, the ratio of the peak to average bore stress, is typically about 4.0. In semicircular keyways, the peak to average stress ratio is somewhat lower, at about 3.0. Nevertheless, it is desirable that the peak to average stress ratio be further reduced.